The present invention relates to a graphic output device of the type effecting antialiasing processing to remove the seps or aliases of jaggy edges of an output image and, more particularly, to a graphic output device capable of effectively outputting image data undergoing antialiasing processing.
In the computer graphic art, an antialiasing technique is used to make an image to appear on an output medium in the form of CRT more attractive. The antialiasing processing is such that the steps of aliases are modulated in luminance to allow an image to appear smooth on a CRT. The data undergone antialiasing may be outputted by a multilevel color laser printer which is usually driven by a power modulation (PM) system or a pulse width modulation (PWM) system. Japanese patent Laid-Open Publication No. 112966/1990 discloses an apparatus which receives bilevel image data in a dot matrix format, recognizes a pattern by dividing the bilevel image data into small areas, and executes correction (antialiasing) with the recognized pattern to thereby improve an image to be displayed. However, a multilevel printer of the type electrostatically forming a latent image by the PM system has a problem that the latent image of each pixel representative of the edge of a figure elongate in the subscanning direction is isolated from the overlying and underlying pixel latent images. The problem with a multilevel printer implemented with the PWM system is that the latent image of each pixel representative of the edge of a figure elongate in the main scanning direction is isolated from the nearby pixel latent images. Moreover, when data undergone antialiasing is outputted by a laser printer, pixels whose luminane is reduced due to modulation cannot be printed out in adequate density. This is especially true when the printing area is small. The apparatus taught in Japanese Patent Laid-Open Publication No. 112966/1990 also lacks the continuity of an image, failing to make the most of the antialiasing procedure.